The operation of an internal combustion engine requires, among other things, the timed opening and closing of a plurality of valves. For example, with a typical four-stroke engine, one of ordinary skill in the art will readily recognize such an engine operates through four distinct strokes of a piston reciprocating through a cylinder, with intake and exhaust valves operating in conjunction with the piston. In an intake stroke, the piston moves from top dead center (TDC) where the piston is near a head portion to bottom dead center (BDC) where the piston is at a predetermined distance from the head. An intake valve is opened allowing air or a fuel and air mixture into the cylinder as the piston travels from TDC to BDC. In a subsequent compression stroke, the piston moves from BDC to TDC while both an exhaust valve and intake valve inhibit gas flow from the cylinder, thereby compressing the air and any residual gasses within the cylinder. A combustion or power stroke follows the compression stroke wherein fuel is injected into the compressed air and thereby ignited. Alternatively, an ignition device such as a spark plug may ignite the mixture of fuel and air. The force resulting from the combustion pushes the piston toward BDC while both the intake and exhaust valves are closed. Finally, the piston reverses direction and moves back toward TDC with the exhaust valve open, thereby pushing the combustion gases out of the cylinder.
Historically, valves on internal combustion engines have been operated in a regular cyclical fashion through the operation of a cam mechanically connected to the valves. Mechanical operation provides an efficient transfer of energy. However, advanced engine cycles may require at least temporary changes in the regular cyclical operation.
As an example, a Miller cycle in an internal combustion engine may be desired to reduce the compression work while maintaining a desired expansion ratio. One method of operating an engine in a Miller cycle closes an intake valve later than provided for by regular cyclical operation of a cam. The exhaust valve may also close later than provided for by the cam to provide internal exhaust gas recirculation (EGR). As known by those skilled in the art, EGR reduces the oxygen available for combustion and reduces formation of an uncertain form of oxides of nitrogen (NOx).
In U.S. Pat. No. 6,237,551 issued to Macor et al. on 29 May 2001, a system is described to vary a duration the valve is in an open position. The cam is connected to a rocker arm to cyclically operate a valve. A hydraulic linkage is placed between the rocker arm and the valves. When activated, the hydraulic linkage allows the rocker arm to move the valve according to a profile of the cam. This system, may also be called a “lost motion” system, allows the valve duration to be shortened by decoupling the cam movement from the valve actuation. The decoupling of the valve from cam allows the valve to return to a valve seat or closed position earlier than produce by the cam movement. However, accidental decoupling or loss of hydraulic pressure will let all valves return to their closed position. The engine in turn will not be able to operate.
As an alternative an actuating mechanism may instead alter the valve movement by acting against the valve to hold the valve as shown in U.S. Pat. No. 6,321,706 issued to Wing on 27 Nov. 2001. In normal operation, the cam cyclically operates on the valve. However, the regular cyclical operation may be altered to extend duration of valve in its open position through the use of various valve holding devices. In one embodiment, a valve member has a shaft extending through a magneto-rheological fluid placed in a sealed chamber. The shaft includes an enlarged portion positioned within the sealed chamber. The valve closing may be delayed by energizing a magnetic field near the chamber to increase the resistance against the enlarged portion moving through the magneto-rheological fluid and delaying closing of the valve. The valve holding device of Wing requires a specifically designed valve shaft and spring arrangement.
The present disclosure is directed to overcoming one or more of the problems or disadvantages associated with the prior art.